The bio-ethanol is one of the most relevant sources of bio-carbon today. This platform molecule available today at a price of its calorific value is venturing out of fuel application being used as precursor for base chemicals. While the ethylene can easily produced by dehydration from ethanol, the direct conversion of ethanol to propylene is problematic due to very low yield.
One step process provides a wide diversity in the formed products obtained in minor amounts which monetizing is not very obvious. Multistep process which includes ethanol dehydration to ethylene, offers better overall selectivity to propylene. However, the obtained ethylene has to be first dimerized to butene or oligomerized to be further reacted via metathesis or via cracking in OCP (olefin cracking process) reactor. The complexity of the multistep process increases significantly the manufacturing costs of bio-propylene.
The way to produce bio-propylene can be accomplished by employing a new concept: using isobutanol as a platform molecule. Of the described routes towards isobutanol, the Guerbet condensation, the synthesis gas conversion to alcohols and the 2-keto acid pathway from carbohydrates are routes that can use biomass as primary feedstock. The fermentation of sugar as well as a syn-gas conversion may result directly to formation of heavy alcohols (C3+), in particular i-butanol, which is often an abundant product (Applied Catalysis A, general, 186, p. 407, 1999 and Chemiker Zeitung, 106, p. 249, 1982).
Gasification of biomass results in synthesis gas that can be converted after purification into methanol, ethanol, propanol or directly into isobutanol. In addition, methanol and ethanol or propanol resourced from biomass can be further condensed to isobutanol. The base-catalysed Guerbet condensation of methanol with ethanol and/or propanol increases the concentration of i-butanol in the alcohol fraction and in particular in C3+ heavy alcohols fraction (J. of Molecular Catalysis A: Chemical 200, 137, 2003 and Applied Biochemistry and Biotechnology, 113-116, p. 913, 2004).
Isobutanol (2-methyl-1-propanol) has historically found limited applications and its use resembles that of 1-butanol. It has been used as solvent, diluent, wetting agent, cleaner additive and as additive for inks and polymers. Recently, isobutanol has gained interest as fuel or fuel component as it exhibits a high octane number (Blend Octane R+M/2 is 102-103) and a low vapor pressure (RVP is 3.8-5.2 psi).
Isobutanol is often considered as a byproduct of the industrial production of 1-butanol (Ullmann's encyclopedia of industrial chemistry, 6th edition, 2002). It is produced from propylene via hydroformylation in the oxo-process (Rh-based catalyst) or via carbonylation in the Reppe-process (Co-based catalyst). Hydroformylation or carbonylation makes n-butanal and iso-butanal in ratios going from 92/8 to 75/25. To obtain isobutanol, the iso-butanal is hydrogenated over a metal catalyst.
Recently, new biochemical routes have been developed to produce selectively isobutanol from carbohydrates. The new strategy uses the highly active amino acid biosynthetic pathway of microorganisms and diverts its 2-keto acid intermediates for alcohol synthesis. 2-Keto acids are intermediates in amino acid biosynthesis pathways. These metabolites can be converted to aldehydes by 2-keto-acid decarboxylases (KDCs) and then to alcohols by alcohol dehydrogenases (ADHs). Two non-native steps are required to produce alcohols by shunting intermediates from amino acid biosynthesis pathways to alcohol production (Nature, 451, p. 86, 2008 and US patent 2008/0261230). Recombinant microorganisms are required to enhance the flux of carbon towards the synthesis of 2-keto-acids. In the valine biosynthesis 2-ketoisovalerate is an intermediate. Glycolyse of carbohydrates results in pyruvate that is converted into acetolactate by acetolactate synthase. 2,4-dihydroxyisovalerate is formed out of acetolactate, catalysed by isomeroreductase. A dehydratase converts the 2,4-dihydroxyisovalerate into 2-keto-isovalerate. In the next step, a keto acid decarboxylase makes isobutyraldehyde from 2-keto-isovalerate. The last step is the hydrogenation of isobutyraldehyde by a dehydrogenase into isobutanol.
The direct 2-keto acid pathway can produce isobutanol from carbohydrates that are isolated from biomass. Simple carbohydrates can be obtained from plants like sugar cane, sugar beet. More complex carbohydrates can be obtained from plants like maize, wheat and other grain bearing plants. Even more complex carbohydrates can be isolated from substantially any biomass, through unlocking of cellulose and hemicellulose from lignocelluloses.
The isobutanol can be dehydrated to corresponding mixture of olefins containing the same number of atoms. Dehydration of butanols has been described on alumina-type catalysts (Applied Catalysis A, General, 214, p. 251-257, 2001).
Both double-bond shift and skeletal isomerisation has been obtained at very low space velocity (or very long reaction time) corresponding to a GHSV (Gas Hourly Space Velocity=ratio of feed rate (gram/h) to weight of catalyst (ml)) of less than 1 gram·ml−1·h−1. The dehydration reactions of alcohols to produce alkenes with the same number of carbons have been known for a long time (J. Catal. 7, p. 163, 1967 and J. Am. Chem. Soc. 83, p. 2847, 1961). Many available solid acid catalysts can be used for alcohol dehydration (Stud. Surf. Sci. Catal. 51, p. 260, 1989), the European patent EP0150832, Bulletin of the Chemical Society of Japan, vol 47(2), 424-429 (1974). However, γ-aluminas are the most commonly used, especially for the longer chain alcohols (with three and more carbon atoms). This is because catalysts with stronger acidity, such as the silica-aluminas, molecular sieves, zeolites or resin catalysts can promote double-bond shift, skeletal isomerization and other olefin inter-conversion reactions.
The primary product of the acid-catalysed dehydration of isobutanol is iso-butene and water:
So, the dehydration may result in substantially pure isobutene stream or in blended olefinic stream reach in butenes if a secondary reaction occurs on the catalyst.
The production of light olefins (ethylene and propylene) from a mixed alcohol feedstock in an oxygenates to olefins process has been described in the U.S. Pat. No. 7,288,689. Said patent provides various processes for producing C1 to C4 alcohols, optionally in a mixed alcohol stream, and optionally converting the alcohols to light olefins. In one embodiment, it includes directing a first portion of a syngas stream to a methanol synthesis zone wherein methanol is synthesized. A second portion of the syngas stream is directed to a fuel alcohol synthesis zone wherein fuel alcohol is synthesized. The methanol and at least a portion of the fuel alcohol are directed to an oxygenate to olefin reaction system for conversion thereof to ethylene and propylene. In this prior art “fuel alcohol” means an alcohol-containing composition comprising ethanol, one or more C3 alcohols, one or more C4 alcohols and optionally one or more C5+ alcohols. At col 21 lines 14+ is mentioned “ . . . Additionally or alternatively, the fuel alcohol-containing stream comprises one or more C4 alcohols, preferably on the order of from about 0.1 to about 20 weight percent C4 alcohols, preferably from about 1 to about 10 weight percent C4 alcohols, and most preferably from about 2 to about 5 weight percent C4 alcohols, based on the total weight of the fuel alcohol-containing stream. The fuel alcohol-containing stream preferably comprises at least about 5 weight percent C3-C4 alcohols, more preferably at least about 10 weight percent C3-C4 alcohols, and most preferably at least about 15 weight percent C3-C4 alcohols . . . ”. Preferably, the molecular sieve catalyst composition comprises a small pore zeolite or a molecular sieve selected from the group consisting of: MeAPSO, SAPO-5, SAPO-8, SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-031, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, AEUCHA intergrowths, metal containing forms thereof, intergrown forms thereof, and mixtures thereof.
EP 2070896 A1 describes the dehydration of 1-butanol on a porous crystalline aluminosilicate (TON type) in the hydrogen form. At 500° C. the products are in wt %:
propylene 10.76
trans-butene-2 16.99
butene-1 13.49
isobutene 31.30
cis-butene-2 13.33
U.S. Pat. No. 6,768,037 describes a process for upgrading a Fischer-Tropsch product comprising paraffins, oxygenates (alcohols), and C6+ olefins. The process includes contacting the Fischer-Tropsch product with an acidic olefin cracking catalyst (ZSM-5) to convert the oxygenates and C6+ olefins to form light olefins. The contacting conditions include a temperature in the range of about 500° F. to 850° F., a pressure below 1000 psig, and a liquid hourly space velocity in the range of from about 1 to 20 hr−1. The process further includes recovering the Fischer-Tropsch product comprising unreacted paraffins, and recovering the light olefins. At col 6 lines 16+ is mentioned “ . . . The product from a Fischer-Tropsch process contains predominantly paraffins; however, it may also contain C6+ olefins, oxygenates, and heteroatom impurities. The most abundant oxygenates in Fischer-Tropsch products are alcohols, and mostly primary linear alcohols. Less abundant types of oxygenates in Fischer-Tropsch products include other alcohol types such as secondary alcohols, acids, esters, aldehydes, and ketones . . . ”.
U.S. Pat. No. 4,698,452 relates to a novel process for the conversion of ethanol or its mixtures with light alcohols and optionally water into hydrocarbons with specific and unusual selectivity towards ethylene. More particularly, it relates to the use of ZSM-5 zeolite based catalysts into which Zn alone or Zn and Mn are incorporated. The preferred reaction conditions used in the experiments are as follows: temperature=300° C.-450° C. (most preferred 400° C.); catalyst weight=4 g; total pressure=1 atm; alcohol or aqueous ethanol pressure=0.9 atm; inert gas (stripping gas)=nitrogen; weight hourly space velocity (W.H.S.V.)=2.4 h-1; duration of a run=4 hours. At table 3 dehydration of isobutanol has been made on ZSM-5 (Zn—Mn) and produces paraffins C1-C4, ethylene, propylene, butenes, aromatics and aliphatics.
It has now been discovered that isobutanol or a mixture of isobutanol and other alcohols containing three and more carbon atoms can be simultaneously dehydrated and cracked to propylene in a one-pot reactor to produce propylene rich feedstock.